mnt: Refactor fs_fully_visible into mount_too_revealing
Replace the call of fs_fully_visible in do_new_mount from before the
new superblock is allocated with a call of mount_too_revealing after
the superblock is allocated. This winds up being a much better location
for maintainability of the code.
The first change this enables is the replacement of FS_USERNS_VISIBLE
with SB_I_USERNS_VISIBLE. Moving the flag from struct filesystem_type
to sb_iflags on the superblock.
Unfortunately mount_too_revealing fundamentally needs to touch
mnt_flags adding several MNT_LOCKED_XXX flags at the appropriate
times. If the mnt_flags did not need to be touched the code
could be easily moved into the filesystem specific mount code.
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/fs/namespace.c b/fs/namespace.c
index 783004a..1a69aa7 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2375,7 +2375,7 @@
return err;
}
-static bool fs_fully_visible(struct file_system_type *fs_type, int *new_mnt_flags);
+static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags);
/*
* create a new mount for userspace and request it to be added into the
@@ -2408,12 +2408,6 @@
flags |= MS_NODEV;
mnt_flags |= MNT_NODEV | MNT_LOCK_NODEV;
}
- if (type->fs_flags & FS_USERNS_VISIBLE) {
- if (!fs_fully_visible(type, &mnt_flags)) {
- put_filesystem(type);
- return -EPERM;
- }
- }
}
mnt = vfs_kern_mount(type, flags, name, data);
@@ -2425,6 +2419,11 @@
if (IS_ERR(mnt))
return PTR_ERR(mnt);
+ if (mount_too_revealing(mnt, &mnt_flags)) {
+ mntput(mnt);
+ return -EPERM;
+ }
+
err = do_add_mount(real_mount(mnt), path, mnt_flags);
if (err)
mntput(mnt);
@@ -3216,22 +3215,19 @@
return chrooted;
}
-static bool fs_fully_visible(struct file_system_type *type, int *new_mnt_flags)
+static bool mnt_already_visible(struct mnt_namespace *ns, struct vfsmount *new,
+ int *new_mnt_flags)
{
- struct mnt_namespace *ns = current->nsproxy->mnt_ns;
int new_flags = *new_mnt_flags;
struct mount *mnt;
bool visible = false;
- if (unlikely(!ns))
- return false;
-
down_read(&namespace_sem);
list_for_each_entry(mnt, &ns->list, mnt_list) {
struct mount *child;
int mnt_flags;
- if (mnt->mnt.mnt_sb->s_type != type)
+ if (mnt->mnt.mnt_sb->s_type != new->mnt_sb->s_type)
continue;
/* This mount is not fully visible if it's root directory
@@ -3298,6 +3294,22 @@
return visible;
}
+static bool mount_too_revealing(struct vfsmount *mnt, int *new_mnt_flags)
+{
+ struct mnt_namespace *ns = current->nsproxy->mnt_ns;
+ unsigned long s_iflags;
+
+ if (ns->user_ns == &init_user_ns)
+ return false;
+
+ /* Can this filesystem be too revealing? */
+ s_iflags = mnt->mnt_sb->s_iflags;
+ if (!(s_iflags & SB_I_USERNS_VISIBLE))
+ return false;
+
+ return !mnt_already_visible(ns, mnt, new_mnt_flags);
+}
+
static struct ns_common *mntns_get(struct task_struct *task)
{
struct ns_common *ns = NULL;